Dr. Stott is conducting a study to determine what 9-year-olds know. Based on theory, he believes that the 9-year-olds will advance in knowledge based on instructions. Dr. Stott's belief is based on:

Dr. Stott's belief about that the 9-year-olds will advance in knowledge based on instructions is based on the theory of cognitive development, proposed by Lev Vygotsky.

Explanation:

Theory of cognitive development - also called the socio-cultural theory of cognition - was put forward by the Russian-Jewish psychologist Lev Vygotsky, in which he expresses the influence of the socio-cultural environment on the learning process.

For Vygotsky, children possess innate basic skills, such as attention, sensation, memory and perception, which develop over time.

The process of cognitive development implies that the development of each child's basic skills requires the guidance of an adult, since - although there are skills that he does not understand or has not developed - he can learn them with the appropriate guidance and instructions.